Fluorescence and absorption in electron beam excited argon

Argon under pressures ranging from 0.5-8 bar was excited by an intense relativistic electron beam. The fluorescence of the Ar₂* excimer radiation at 126 nm and of the Ar*(4p) to Ar*(4s) transitions in the visible as well as the transient absorption between 200 and 600 nm have been studied. The analysis of the results leads to a kinetic model which accounts for all observed features. For high excitation densities Ar₂*(1_u, O_mu ^-) is determined to be the main absorber in the near UV. Cross sections for photoabsorption in Ar₂*(1_u,O_u^-) are given. The so-called 'background' absorption is identified to be caused mainly by photoionisation of Ar*(4p) and photodissociation of vibrationally excited Ar₂⁺.